Mechanical circulatory support has been used successfully in adults as a long-term bridge to transplantation and as destination therapy for more than three decades. In recent years, a small number of devices has been used to provide circulatory support in the pediatric population. A wide range of complications have been associated with use of mechanical circulatory assist systems in pediatric patients, with thrombosis and the related complications hemorrhage and stroke occurring most frequently. Because of their small diameters and low flow rates through them, it is likely that the cannulas used with pediatric circulatory assist devices are a preferential site of thromboembolism initiation. Luna Innovations and the Cardiovascular Biomaterials Laboratory at Pennsylvania State University propose to develop and commercialize plateletresistant, sub-micron textured, small diameter cannulas from a biomedical polyurethane material. Specifically, prototype small diameter poly(urethane urea) cannulas will be fabricated with sub-micron inner surface topographic patterns and tested in platelet rich plasma in an in vitro flow loop designed to simulate pediatric circulatory assist device flow patterns. The central hypothesis is that a properly designed surface topography that significantly limits the platelet-accessible contact area under low flow conditions will lead to a reduction in initial platelet adhesion, subsequent platelet activation, and ultimate likelihood of surfaceinduced thrombus formation.